Is there a difference between antioxidants in different foods?

Probably. There was a recent dutch study done to try to investigate the benefits of different types of fruits and vegetables, which they grouped by color. The "white fruits, " including apples and pears, showed a very strongly positive benefit in reduction of the risk of stroke. The authors found that other fruit groups might have different benefits that weren't specifically tracked in that study.
Concentration & type. Different foods have different types and concentration of antioxidants. That's why it's important to eat a healthy, balanced diet and a good mix of fruits and vegetables.